title: Characterization of trans-septal activation during septal pacing: criteria for identification of intramural ventricular tachycardia substrate in nonischemic cardiomyopathy.
abstract: BACKGROUND
  Identification of intramural basal-septal ventricular tachycardia (VT) substrate is challenging in nonischemic cardiomyopathy. We sought to (1) characterize normal/abnormal trans-septal right ventricular (RV) to left ventricular activation; (2) assess the effect of opposite RV pacing on left ventricular septal bipolar electrograms (EGMs); and (3) establish criteria for the identification of intramural septal VT substrate.
  
  
  RESULTS
  Endocardial activation mapping and local EGM assessment of the left interventricular septum was performed during RV basal septal pacing in 40 patients undergoing VT ablation with no evidence of septal scar (group 1, n=14) and with septal scar (group 2, n=26) defined by low septal unipolar voltage (<8.3 mV) and delayed enhancement on cardiac MRI with/without abnormal bipolar voltage (<1.5 mV) in sinus rhythm. Left ventricular trans-septal activation time was prolonged in Group 2 compared with Group 1 (55.3±33.0 versus 25.7±8.8 ms; P=0.003). In 6 group 2 patients, left ventricular septal breakthrough was displaced to the scar border. During RV pacing, group 2 had fractionated (8.8%), late (2.8%), and split (5.7%) EGMs not seen in group 1. Trans-septal activation >40 ms (sensitivity 60%, specificity 100%; P<0.001) and EGM duration >95 ms during pacing (sensitivity 22%, specificity 91%; P<0.001) identified septal scar (13/26 pts).
  
  
  CONCLUSIONS
  In patients with nonischemic cardiomyopathy, VT and septal scar, delayed transmural conduction time (>40 ms) and fractionated, late, split, and wide (>95 ms) bipolar EGMs during RV basal pacing identify intramural VT substrate. In select cases, the basal septum appears compartmentalized as the stimulated wavefront is rerouted to the scar border.
authors.affiliation: Division of Cardiac Electrophysiology and Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia.
authors.forename: Brian P
authors.initials: BP
authors.lastname: Betensky
authors.forename: Suraj
authors.initials: S
authors.lastname: Kapa
authors.forename: Benoit
authors.initials: B
authors.lastname: Desjardins
authors.forename: Fermin C
authors.initials: FC
authors.lastname: Garcia
authors.forename: David J
authors.initials: DJ
authors.lastname: Callans
authors.forename: Sanjay
authors.initials: S
authors.lastname: Dixit
authors.forename: David S
authors.initials: DS
authors.lastname: Frankel
authors.forename: Mathew D
authors.initials: MD
authors.lastname: Hutchinson
authors.forename: Gregory E
authors.initials: GE
authors.lastname: Supple
authors.forename: Erica S
authors.initials: ES
authors.lastname: Zado
authors.forename: Francis E
authors.initials: FE
authors.lastname: Marchlinski
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial; D009202:Cardiomyopathies / Q000503:physiopathology*; D022062:Electrophysiologic Techniques, Cardiac / Q000379:methods*; D056149:Epicardial Mapping / Q000379:methods; D005260:Female; D006346:Heart Septum / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017180:Tachycardia, Ventricular / Q000503:physiopathology*
keywords: mapping; tachycardia, ventricular